refactor(dnd): remove drag-and-drop reorder for stories and tasks

- Remove reorderStoriesAction, reorderTasksAction, reorderSprintStoriesAction
- Delete REST route app/api/stories/[id]/tasks/reorder/route.ts
- Remove DnD from backlog story-panel and task-panel (flat list)
- Remove reorder-within-sprint branch from sprint-board-client handleDragEnd
- Switch SortableSprintRow to plain SprintRow using useDraggable (membership drag kept)
- Remove all DnD from task-list (status toggle + edit kept)
- Remove story-order/task-order/sprint-story-order/sprint-task-order mutation types and store handlers
- Remove related tests for deleted reorder route; fix sprint store tests

components/backlog/task-panel.tsx

@@ -1,27 +1,6 @@
 'use client'
 
-import { useState, useTransition } from 'react'
 import { useRouter } from 'next/navigation'
-import {
-  DndContext,
-  DragEndEvent,
-  DragOverlay,
-  DragStartEvent,
-  KeyboardSensor,
-  PointerSensor,
-  useSensor,
-  useSensors,
-  closestCenter,
-} from '@dnd-kit/core'
-import {
-  SortableContext,
-  useSortable,
-  rectSortingStrategy,
-  arrayMove,
-  sortableKeyboardCoordinates,
-} from '@dnd-kit/sortable'
-import { CSS } from '@dnd-kit/utilities'
-import { toast } from 'sonner'
 import { Badge } from '@/components/ui/badge'
 import { Button } from '@/components/ui/button'
 import { PanelNavBar } from '@/components/shared/panel-nav-bar'
@@ -33,7 +12,6 @@ import type {
   BacklogTask,
   TaskDetail,
 } from '@/stores/product-workspace/types'
-import { reorderTasksAction } from '@/actions/tasks'
 import { BacklogCard } from './backlog-card'
 import { debugProps } from '@/lib/debug'
 import { EmptyPanel } from './empty-panel'
@@ -52,32 +30,17 @@ const STATUS_LABELS: Record<string, string> = {
   DONE: 'Klaar',
 }
 
-function SortableTaskCard({
+function TaskCard({
   task,
-  isDemo,
   onClick,
 }: {
   task: BacklogTask | TaskDetail
-  isDemo: boolean
   onClick: () => void
 }) {
-  const { attributes, listeners, setNodeRef, transform, transition, isDragging } =
-    useSortable({ id: task.id })
-
-  const style = {
-    transform: CSS.Transform.toString(transform),
-    transition,
-  }
-
   return (
     <BacklogCard
-      ref={setNodeRef}
-      style={style}
-      {...attributes}
-      {...(isDemo ? {} : listeners)}
       title={task.title}
       priority={task.priority}
-      isDragging={isDragging}
       onClick={onClick}
       badge={
         <Badge
@@ -99,64 +62,17 @@ interface TaskPanelProps {
   closePath: string
 }
 
-// PBI-74 / T-851: leest tasks voor active story via selectTasksForActiveStory
-// (useShallow). DnD via applyOptimisticMutation('task-order'). Detail-view
-// (ensureTaskLoaded + isDetail()) zit in de task-dialog, niet in deze lijst.
+// PBI-74 / T-851: leest tasks voor active story via selectTasksForActiveStory.
 export function TaskPanel({ isDemo, closePath }: TaskPanelProps) {
   const router = useRouter()
-  const [, startTransition] = useTransition()
   const selectedStoryId = useProductWorkspaceStore((s) => s.context.activeStoryId)
   const rawTasks = useProductWorkspaceStore(useShallow(selectTasksForActiveStory)) as
     | (BacklogTask | TaskDetail)[]
-  const [activeDragId, setActiveDragId] = useState<string | null>(null)
 
   const tasks: (BacklogTask | TaskDetail)[] | null = selectedStoryId
     ? rawTasks
     : null
 
-  const sensors = useSensors(
-    useSensor(PointerSensor, { activationConstraint: { distance: 5 } }),
-    useSensor(KeyboardSensor, { coordinateGetter: sortableKeyboardCoordinates }),
-  )
-
-  function handleDragStart(event: DragStartEvent) {
-    setActiveDragId(event.active.id as string)
-  }
-
-  function handleDragEnd(event: DragEndEvent) {
-    setActiveDragId(null)
-    if (!selectedStoryId || !tasks) return
-    const { active, over } = event
-    if (!over || active.id === over.id) return
-
-    const store = useProductWorkspaceStore.getState()
-    const prevOrder = [...(store.relations.taskIdsByStory[selectedStoryId] ?? [])]
-    const oldIndex = prevOrder.indexOf(active.id as string)
-    const newIndex = prevOrder.indexOf(over.id as string)
-    if (oldIndex === -1 || newIndex === -1) return
-    const newOrder = arrayMove([...prevOrder], oldIndex, newIndex)
-
-    const orderMutationId = store.applyOptimisticMutation({
-      kind: 'task-order',
-      storyId: selectedStoryId,
-      prevTaskIds: prevOrder,
-    })
-    useProductWorkspaceStore.setState((s) => {
-      s.relations.taskIdsByStory[selectedStoryId] = newOrder
-    })
-
-    startTransition(async () => {
-      const result = await reorderTasksAction(selectedStoryId, newOrder)
-      const st = useProductWorkspaceStore.getState()
-      if (result?.error) {
-        st.rollbackMutation(orderMutationId)
-        toast.error(result.error)
-      } else {
-        st.settleMutation(orderMutationId)
-      }
-    })
-  }
-
   const navActions = (
     <DemoTooltip show={isDemo}>
       <Button
@@ -201,42 +117,19 @@ export function TaskPanel({ isDemo, closePath }: TaskPanelProps) {
     )
   }
 
-  const activeTask = activeDragId ? tasks.find((t) => t.id === activeDragId) : null
-
   return (
     <div className="flex flex-col h-full" {...dp}>
       <PanelNavBar title="Taken" actions={navActions} />
       <div className="flex-1 overflow-y-auto p-3">
-        <DndContext
-          id="task-panel"
-          sensors={sensors}
-          collisionDetection={closestCenter}
-          onDragStart={handleDragStart}
-          onDragEnd={handleDragEnd}
-        >
-          <SortableContext items={tasks.map((t) => t.id)} strategy={rectSortingStrategy}>
-            <div className="grid grid-cols-2 gap-2">
-              {tasks.map((task) => (
-                <SortableTaskCard
-                  key={task.id}
-                  task={task}
-                  isDemo={isDemo}
-                  onClick={() => router.push(`${closePath}?editTask=${task.id}`)}
-                />
-              ))}
-            </div>
-          </SortableContext>
-
-          <DragOverlay>
-            {activeTask && (
-              <BacklogCard
-                title={activeTask.title}
-                priority={activeTask.priority}
-                className="border-primary shadow-xl opacity-90"
-              />
-            )}
-          </DragOverlay>
-        </DndContext>
+        <div className="grid grid-cols-2 gap-2">
+          {tasks.map((task) => (
+            <TaskCard
+              key={task.id}
+              task={task}
+              onClick={() => router.push(`${closePath}?editTask=${task.id}`)}
+            />
+          ))}
+        </div>
       </div>
     </div>
   )